I. Field of Invention
The invention relates to suppression of cross-polarization interference in communications systems in which orthogonal channels are used. More particularly, the invention relates to orthogonal code division multiple access (OCDMA) communications systems in which the same long code is used in both polarization channels (for example, left hand channel and right hand channel), while substantially maintaining cross-polarization interference suppression.
II. Related Art
In conventional communications systems, it is known to simultaneously use left and right polarizations to increase capacity. Channels within each polarization may be made orthogonal using, for example, Walsh code techniques. Conventional wisdom with CDMA (code division multiple access) further teaches use of randomization (for example, by long code spreading) to help combat such problems as interference at boundaries of cells or sectors, multipath problems, and so forth. However, conventional long code spreading, involving distinct long codes for orthogonal channels, does not appear to result in the optimum signal to interference-plus-noise ratio (SINR).
Accordingly, there is a need in the art to provide an arrangement for effectively maximizing SINR (and, by implication, minimizing frame error rate (FER)), thus providing a higher theoretical throughput for a given overall noise and interference environment.